Integrated circuits (IC) devices are usually fabricated on semiconductor wafers which have a plurality of IC device die each including bond pads on its top surface that connect to various nodes in the device, such as for signal input, signal output and power supply nodes. The bond pads are generally connected by a bond wire of a lead frame or other electrically conductive structure such as a contact pad on a support such a printed circuit board (PCB) to permit utilization of the IC die. Known methods for connecting an IC device to a lead frame or other support include wire bonding, Tape Automated Bonding (TAB), Controlled Collapse Chip Connection (C4) or bump bonding, and electrically conductive adhesives.
To provide a reliable and low electrical resistance attachment to the bond pad surface, some packaging technologies have used multi-layered bond pads having a top metal layer that is both electrically conductive and resistant to oxidation to provide high reliability (good corrosion performance) and high performance (low resistance). One such bond pad arrangement deposits a dielectric passivation layer(s) over an oxidizable uppermost metal interconnect layer such as copper or aluminum, and then forms a trench including dielectric sidewalls from the passivation layer. A barrier layer comprising a refractory metal (e.g., Ta, TaN, or Ti) is then deposited that lines the passivation sidewalls which provides good adhesion to the passivation material. A multi-layer metal stack is formed on the barrier layer which in one particular embodiment can comprise palladium (Pd) as the final (top) layer on a nickel layer over the uppermost metal interconnect layer to provide a stable surface for wire bonding. Pd being a platinum group metal has a low propensity for oxidation and is a good outer capping layer for the bond pad to prevent chemical attack of the oxidizable uppermost metal interconnect layer material thereunder.
Some IC devices have aluminum bond pads. Solder bumping on aluminum is known to generally not be possible due to aluminum oxide formation during the soldering process which prevents solder adhesion. As a result, conventional solder bump processes for soldering to aluminum bond pads generally require forming a complex stack on the aluminum including a refractory-metal based barrier layer then a copper seed, followed by an electroplated copper redirect layer (RDL) then under bump metallization (UBM) thereon, where the solder bump (or ball) is then formed on the UBM.